The present application is related to the alignment of vehicles wheels located on an axle, such as passenger cars, trucks, trailers, or semi-trailers and in particular, to a method for detecting slip of an angle sensor or optical target mounted to vehicle wheels on an axle during the course of an alignment measurement process.
Many vehicle wheel alignment systems, such as those for heavy duty vehicles such as trucks, buses, and tractor trailers, rely upon angle sensors or optical targets which are secured to the individual wheels of the vehicle by mounting adapters during an alignment measurement procedure. There are a variety of methods for securing the mounting adapters to the vehicle wheels, most of which require some means for clamping, gripping, or temporarily engaging a surface of the wheel assembly tire, rim, lug nuts/bolts, or wheel hub component. Accurate measurements of vehicle wheel alignment angles necessitate that the angle sensors or optical targets which are coupled to the adapters remain in a fixed position relative to the wheel assembly on which they are secured during the measurement process.
When adjusting the alignment angles of vehicles, such as the trailers and semi-trailers shown in FIGS. 1 and 2, or a tow vehicle, such as shown in FIG. 3, each with one or more axles coupling wheels on opposite lateral sides, it is not uncommon for significant forces to be exerted directly (or indirectly) against the axles, axle brackets, or attachment means securing the axles to the vehicle frames. For example, the use of impact wrenches to loosen bolts, hammers to shift components, or pry bars exerting leverage against an axle or axle component, or even against other interconnected components on the vehicle, can all impart significant force to the vehicle axle, and can induce large vibrations therein. At other times during the alignment measurement or inspection procedures, the vehicle may be rolled short distances, which rotates the mounting adapters together with the associated vehicle wheels about their respective axis of rotation. The forces exerted on, and vibrations experienced by, an axle during adjustment and/or rolling movement can cause an improperly secured mounting adapter to slip or move relative to the vehicle wheel assembly to which it is secured. This movement may be sufficiently small to be unnoticed by a human operator, while still being statistically significant in terms of altering the alignment angles measured using the associated angle sensor or optical target. If the slip or movement remains undetected and/or uncorrected, the resulting alignment angle measurements for the vehicle will be inaccurate, and may lead to further incorrect adjustments to the vehicle while failing to correct a true misalignment.
Accordingly, there is a need for vehicle wheel alignment measurement systems, and in particular, for those systems adapted for use with vehicles having one or more axles, to provide a method by which mounting adapter slip or movement may be detected during the course of an alignment measurement and adjustment procedure.